Our studies show that IFN-lambda sustains the activation of the signal transducers and activators of transcription: STAT1 and STAT2 for longer than 8 hours. This is a striking difference from the activation profile of these transcription factors when activated by type I IFNs. Interestingly the kinetics of gene activation between type I and type III IFNs are not the same. Rather, type I IFNs induce gene transcription earlier while IFN-lambda mediated gene transcription is not only delayed but sustained longer. In addition, IFN-lambda is better than IFN-alpha in inducing an antiproliferative effect on tumor cells. These findings highlight the potential therapeutic use of IFN-lambda in the treatment of cancer. Our goal is to test the antitumor and antimetastatic effects of this cytokine in mouse tumor models.